The main objective of this study is to investigate the effect of pilot-, post- and multiple-fuel injection strategies on fuel-air mixing and emissions formation in diesel combustion, using a combination of experimental observations and Computational Fluid Dynamics (CFD) analysis. The experimental study was carried out on a single-cylinder optical direct-injection diesel engine equipped with a high pressure common rail fuel injection system. The experimental work was supported by CFD simulations on the single-cylinder engine in order to investigate the effect of multiple injections on mixture formation. The limitations of the soot formation model were identified through direct comparisons with experimental flame visualization.